Weeks after a Russian passenger plane crashed in Egypt's Sinai Province, Russia has confirmed that it was downed in a terror attack.
The Islamic State had claimed responsibility for the crash, claiming that it had shot the plane down.
However, Russian Federal Security Service (FSB) chief Alexander Bortnikov said on Tuesday that a homemade explosive device was placed on the plane that caused it to explode and break mid-air while it was flying from the popular Sharm el-Sheikh resort on the Red Sea to St Petersburg.
He said that the bomb was equivalent of up to one kg of TNT, Russia's Tass news agency reported.
Russian President Vladimir Putin has vowed to 'find and punish' those behind the terror act, according to the news agency.
"The murder of our nationals in Sinai is among the bloodiest crimes as to the number of casualties. We will be searching them (terrorists) everywhere, no matter where they hide. We will find them in any point of the globe and they will be punished," Putin said.
Russia has also announced a reward of $50 million to anyone who provides information about those responsible for the crash.
The Russian airline Kogalymavia plane crashed in the Sinai desert on 31 October, killing all 224 people on board.
Several terror experts had named Abu Osama al-Masri, an Egyptian cleric who heads Isis branch in Sinai, to be the mastermind.
The Islamic State, which is active in the restive Sinai province in Egypt, had released a video after the crash claiming that it shot down the plane in retaliation to Russian airstrikes against Isis targets in Syria.